Does the writing of the Prophet's (peace be upon him) biography 130 years after his death, its reliance on oral روایت, and its not being free from potential political influences by the caliphs, make it susceptible to deceit, distortion, or a reduction in its authenticity?

This statement holds no scientific weight. Books of Sīrah (Prophetic biography) are not the primary source for the Prophet's biography, and not everything narrated by Ibn Ishaq is acceptable. The criterion for accepting narrations relies on the authenticity of their chains of transmission (isnāds), and this applies to all books that include isnāds, such as Sahih al-Bukhari. Ibn Hisham's abridgement of Ibn Ishaq's Sīrah did not negate the original. Ibn Hisham explicitly stated that he omitted poems unknown to scholars of poetry and other matters unrelated to the Sīrah. The primary source for the Prophet's biography is the Holy Qur'an, followed by reliable Hadith books, and then books of Sīrah and history. The omitted poems, which contained slanders against the Prophet, serve as proof against the falsity of the accusation that Ibn Ishaq was flattering the Caliph.